Pseudomonas keratitis is now perhaps the most important bacterial infection of the human cornea. The infection is rapidly progressive and high destructive. Little is known about the pathogenesis of infection or the role of various host defense mechanisms. The results of chemotherapy are poor. We have developed an experimental model of Pseudomonas keratitis that is suitable for quantitative investigation. We have made considerable progress in our studies on the pathogenesis and chemotherapy of infection. We propose to continue our research on pathogenesis and treatment of corneal infection as determined by clinical inspection, biomicroscopy, light and electron microscopy and quantitative bacterial sub-cultures. One broad objective is to identify host factors and bacterial products that contribute to corneal damage. We will evaluate effects of leukocytes and complement components, as well as exotoxin A, protease, endotoxin, and slime. A second broad objective is to determine the optimal therapy of Pseudomonas keratitis. Agents to be evaluated include antibiotics, chelating agents, enzyme inhibitors, corticosteroids, active and passive immunity, and cryotherapy. The studies we propose will provide, in part, a firm experimental basis for the design of controlled therapy trials in humans.